The invention relates to the field of chemotherapeutic treatment and particularly to a method of predicting the clinical response to chemotherapeutic treatment with alkylating agents for the treatment of certain tumor types.
Systemic chemotherapy is the primary treatment available for certain types of tumors and malignant diseases. Curative chemotherapeutic regimens and palliative chemotherapeutic regimens have been developed for many tumor types, often resulting in improved survival. Chemotherapy, whether given with curative or palliative intent, usually requires multiple cycles of treatment. Every chemotherapeutic regimen administered in adequate doses will have some deleterious side effect on normal host tissues.
Chemotherapeutic efficacy, the ability of chemotherapy to eradicate tumor cells without causing lethal host toxicity, depends of drug selectivity. The basis for anticancer drug selectivity is not completely understood. One class of anticancer drugs, alkylating agents, cause cell death by binding to DNA which structurally distorts the DNA helical structure preventing DNA transcription and translation. In normal cells, the damaging action of alkylating agents can be repaired by cellular DNA repair enzymes, in particular O6-methylguanine-DNA methyltransferase (MGMT). The level of MGMT varies in tumor cells, even among tumors of the same type. The gene encoding MGMT is not commonly mutated or deleted. Rather, low levels of MGMT in tumor cells is due to an epigenetic modification; the MGMT gene is methylated preventing expression of MGMT.
Methylation has been shown by several lines of evidence to play a role in gene activity, cell differentiation, tumorigenesis, X-chromosome inactivation, genomic imprinting and other major biological processes. In eukaryotic cells, methylation of cytosine residues that are immediately 5xe2x80x2 to a guanosine, occurs predominantly in cytosine-guanine (CG) poor regions. In contrast, CpG islands remain unmethylated in normal cells, except during X-chromosome inactivation and parental specific imprinting where methylation of 5xe2x80x2 regulatory regions can lead to transcriptional repression. Expression of a tumor suppressor gene can also be abolished by de novo DNA methylation of a normally unmethylated CpG.
Hypermethylation of genes encoding DNA repair enzymes can serve as markers for predicting the clinical response to certain cancer treatments. Certain chemotherapeutic agents inhibit cellular proliferation by cross-linking DNA, resulting in cell death. Treatment efforts with such agents can be thwarted because DNA repair enzymes remove the cross-linked structures. In view of the deleterious side effects of most chemotherapeutic drugs, and the ineffectiveness of certain drugs for various treatments, it is desirable to predict the clinical response to treatment with chemotherapeutic agents. The present invention satisfies that need and others.
The present invention is based on the finding that the methylation state of a gene encoding a DNA repair enzyme is predictive of the clinical response to treatment with certain chemotherapeutic agents. Hypermethylation of the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) results in low levels of MGMT. Tumor cells treated with chemotherapeutic agents that cause damage to DNA do not survive because the MGMT is not available to repair the damage.
In one embodiment of the invention, there is provided a method of predicting a clinical response to treatment with a chemotherapeutic agent of a subject in need of treatment. The method includes determining the state of methylation of a nucleic acid isolated encoding a DNA repair enzyme from the subject. The repair enzyme impedes an activity of the chemotherapeutic agent. The state of methylation of the nucleic acid isolated from the subject in need of treatment with the state of methylation of a nucleic acid encoding the same enzyme from a subject not in need of treatment. A difference in the state of methylation is predictive of the clinical response to treatment with a therapeutic agent.
In another embodiment of the invention, there is provided a method of treating a cellular proliferative disorder with an alkylating chemotherapeutic agent in a subject that includes predicting a clinical response to treatment by determining the state of methylation of a nucleic acid encoding a DNA repair enzyme isolated from the subject. The enzyme impedes an activity of the chemotherapeutic agent. The state of methylation of the nucleic acid of the subject compared with the state of methylation of the nucleic acid from a subject not in need of treatment is indicative of the level of enzyme and the response to treatment.
In yet another embodiment of the invention there is provided a kit for predicting the response to chemotherapeutic treatment of a cellular proliferative disorder in a subject. The kit contains a reagent that modifies unmethylated cytosine nucleotides and at least one primer pair including sense primer and at least one antisense for amplification of CpG-containing nucleic acid in the regulatory region of O6-methylguanine-DNA methyltransferase. The primers can distinguish between modified methylated and non-methylated nucleic acid.